Demountable electron gun



Patented May 11, 1943 DEMOUN TABLE ELECTRON GUN James Hillier, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 31, 1941, Serial No. 376,758

11 Claims.

This invention relates to demountable electron guns and especially to a demountable and adjustable electron gun for electron microscopes and similar devices.

Many electron guns, especially those of elec tron microscopes, are preferably demountable. The demountable feature makes it easy to replace a defective cathode. The original gun, as well as the gun with a replaced cathode, must be carefully aligned to avoid undesired distortion in the miscroscope, diffraction camera, or the like. The prior art demountable gun were difficult to align with respect to the axial line of the device in which the gun was used.

The instant invention has for one of its objects the provision of means for aligning a demountable electron gun. Another object is the provision of an electron gun with independent means for aligning and positioning the beam of electrons from the gun with respect to a desired line. Another object is to provide means in a demountable electron gun for aligning the gun and positioning the gun respectively and independently with respect to given axial line.

The invention will be described by referring to the accompanying drawing in which Figure 1 is a sectional view, taken along the line I-I of Fig. 2; Figure Sis a sectional view taken along the line IIII of Fig. 1; and Figure 3 is a detailed sectional view of the cathode. Similar reference characters will be applied to similar elements in the drawing.

Referring to the drawing on a flanged base I are mounted a vacuum tight window 3, an apertured fluorescent screen 5, and a connecting tube 1. An adjustable member 9 is mounted on top of the flanged base I. The upper portion of the adjustable member 9 is made to correspond to a hollow spherical portion II, whose function is hereinafter described. A second adjustable member [3, having a V-shape projected portion I5 which engages the spherical portion II, is mounted on the first member 9. A hollow cylindrical piece I! is tightly connected to the upper bearing plate. An apertured anode electrode I9 is suitably clamped to the upper portion of the cylindrical piece. A flexible member or bellows 2| is suitably connected between the cylindrical piece and the connecting tube 7 to form a flexible and, at the same time, vacuum tight connection between the base and second adjustable member I3. A flanged pump connection 23 joins the connecting tube 1 and a vacuum pump 25.

An insulated tube 2'! is mounted, vacuum tight,

on an annular member 29. The annular member 29 is suitably clamped to the upper surface of the second adjustable member I3. An apertured disc 3i is fastened, vacuum tight, to the upper end of the insulated tube. The cathode electrode 33 of the un is mounted within a tube 3.5, or the like. The tube 35 is inserted through the aperture of the disc 3i and securedthereto by an annular member 3?. Shields 39, 4! are pref? erably secured at the upper andlower ends, respectively, of the insulated tube 27 and are connected to cathode and anode, respectively, to prevent corona discharge of the high voltage source between the cathode and anode.

Four adjusting screws 43, are arranged, preferably at intervals, in a flanged portion 45 of the second adjustable member I 3. Another set of adjusting screws #31 is similarly arranged on'a flanged portion 49 of the first adjustable member 9. The adjusting screws 43, attached to the second member I3, are for moving the second member with respect to the spherical surface II. Since the emissive portion of thecathode 33 is located at the center of curvature of the spher-' ical portion, the direction of the beam of elec trons may be readily adjusted with respect to the axial line 5| of the base I. While the electron beam is somewhat diffused at the fluorescent screen 5, electrons impinging on the screen provide some indication of the nature of the beam and its direction. The optimum adjustment is obtained by means of the second'member I3 which is oriented to make the electron beam parallel the axial line. The parallel adjustment having been secured, the center of the beam may be made to coincide with the axial line 5| by adjusting the screws 41.

The independence of the two adjustments permits the user to readily align the beam without having the successive adjustments upset each other; That is, the adjustment of the upper or second member I3 on the spherical surface is to obtain the desired direction of the beam without regard to its location. The adjustment of the lower member 9 is to locate the beam with respect to the axial line or any desired reference position. These adjustments are independent of each other.

The portion of the gun including the cathode is made with a vacuum tight bellows 53 connection between the cathode and the upper portion of the gun. This connection permits the cathode to be raised or lowered. If a cathode is replaced, the replacement cathode may be readily adjusted so that the emissive portion coincides with the center of curvature of the spherical portion of the second member 13. The cathode is connected to the insulated terminal at the center of the gun and to the shell of the gun. The details of one suitable cathode are shown in Fig. 3.

Thus, the invention has been described as a demountable gun. The gun is mounted on a base which may be a portion of the device employing the gun. Flexible vacuum tight connections are provided between the base and the adjustable parts of the gun. One of the adjustable members is arranged to locate the electron beam with respect to a reference line or position; another adjustable member is arranged to provide a directional alignment independent of the location alignment; and finally an adjustable cathode is provided. What is claimed is:

=1. A demountable electron gun including in combination a base, a member adjustably mounted on said base and including a hollow spherical portion, a second member adjustably mounted on said spherical portion, an electron gun including a cathode and an anode mounted on said second member, and a flexible member connected between said base and said second member and forming a vacuum tight connection therebetween. 2. A demountable electron gun including in combination a base, a member adjustably mounted on said base and including a hollow spherical portion, means for adjusting said adjustable member with respect to said base, a second member adjustably mounted on said spherical portion, an electron gun including a cathode and an anode mounted on said second member, and a flexible member connected between said base and said second member and forming a, vacuum tight connection therebetween. 3. A demountable electron gun including in combination a base, a member adjustably mountedon said base and including a hollow spherical portion, means for adjusting said adjustable member with respect to said base, a second member adjustably mounted on said spherical portion, means for adjusting said second member with respect to said spherical portion, an electron gun including a cathode and an anode mounted on said second member, and a flexible member connected between said base and said second member and forming a vacuum tight connection therebetween.

'4. A demountable electron gun including in combination a base, a member adjustably mounted on said base and including a hollow spherical portion, a second member adjustably mounted on said spherical portion, an electron gun mounted on said second member and including a demountable cathode, and a flexible member connected between said base and said second member and forming a vacuum tight connection therebetween.

5. A demountable electron gun including in combination a base, a member adjustably mounted on said base and including a hollow spherical portion, a second member adjustably mounted on said spherical portion, a cathode mounted on said second member, an anode electrode mounted on said second member and interposed between said cathode and said base, and a flexible member connected between said base and said second member and forming a vacuum tight connection therebetween.

6. In a demountable electron gun the combination of a base, a member mounted on said base and including a hollow spherical portion and means for adjusting said member in a plane normal to the axial line of said base, a second mem ber mounted on said spherical portion and including means for adjusting said second member with respect to said spherical portion, an electron gun mounted on said second member, and a flexible member connected between said base and said second member and forming a vacuum tight connection therebetween.

7 In a demountable electron gun the combination of a base, a member mounted on said base and including a hollow spherical portion and means for adjusting said member in a plane normal to the axial line of said base, a second member mounted on said spherical portion and including means for adjusting said second member With respect to said spherical portion, an electron gun mounted on said second member and including a cathode located substantially at the center of curvature of said spherical portion, and a flexible member connected between said base and said second member and forming a vacuum tight connection therebetween.

8. In a demountable electron gun the combination of a base, a member mounted on said base and including a hollow spherical portion and means for adjusting said member in a plane normal to the axial line of said base, a second member mounted on said spherical portion and including means for adjusting said second member with respect to said spherical portion, an electron gun mounted on said second member and including a cathode located substantially at the center of curvature of said spherical portion, an anode mounted on said second member and including an aperture substantially in alignment with said cathode, and a flexible member connected between said base and adapted for aligning an electron beam from said gun with said axial base line and said second member and forming a vacuum tight connection therebetween.

9. A device of the character of claim 1 including an adjustable cathode electrode located within said electron gun.

10. A device of the character of claim 6 including an adjustable cathode electrode located within said electron gun.

11. A device of the character of claim 7 including means for adjusting the position of said cathode with respect to said center of curvature.

JAMES HILLIER. 

